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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
(a) Substructures 1a, 1b, and 1c defined for compound 1 and full planar structure; key COSY correlations are shown with bold bonds and key HMBC correlations with arrows; (b) key NOESY correlations observed for compound 1.